Numerous methods and materials exist for the construction of retaining walls and landscaping walls. Such methods include the use of natural stone, poured in place concrete, masonry, and landscape timbers or railroad ties. Segmental concrete retaining wall blocks which are dry stacked (i.e., built without the use of mortar) have become a widely accepted product for the construction of retaining walls. Such products have gained popularity because they are mass produced, and thus relatively inexpensive. They are structurally sound, easy and relatively inexpensive to install, and couple the durability of concrete with the attractiveness of various architectural finishes.
These wall blocks are generally produced in a mold assembly which usually consists of a mold box consisting of side frame and end frame walls forming an enclosed cavity, which rests on a production pallet or plate. The mold box assembly may contain one or multiple mold cavities which are configured to provide the block with a desired size and shape and thus may include the use of wall liners, cores and core bars, division plates, etc., as known in the art. A mixture or fill, generally of concrete material, is then poured or loaded into the mold cavities by a feed drawer that has received said material from a batching hopper. The feed drawer moves the fill over the top of the mold box assembly and dispenses the mixture into the mold cavities. As the fill is dispensed, a vibration system may be employed to shake the mold box assembly, thus providing compaction of the loose fill material to form a solid mold block. This vibration system functions to consolidate the concrete material within the mold cavities to produce a more homogeneous concrete product.
After the concrete is dispensed into the mold cavities, the feed drawer retracts rearward from over the top of the mold box assembly. Rigidly coupled on the front of the feedbox is generally a cut-off bar that strikes off and levels the mixture in the mold prior to compaction by the vibration function and stripper shoe compression head assembly producing a generally horizontal level surface. Since the cut-off bar is rigidly coupled to the feed drawer it must follow the generally horizontal path of the feed drawer. Blocks formed from the mold cavities have varying shapes and angles which may require the mix material to be distributed in different proportions from one mold cavity to another, so there is no weakening or compromising of the structural integrity and/or strength of the block from under-filling or over-filling of certain portions of the mold cavities. Since the cut-off bar follows the horizontal path of the feed drawer there is not a suitable means for distributing and leaving additional material in one portion of the mold cavity or less material in another portion of the mold cavity as may be necessary/optimal depending upon the shape and size of the block being produced. There is a need in the art for a cut-off bar that is not rigidly attached to the feed drawer and which can remove and/or redistribute varying amounts of material as necessary to all portions of the mold box cavity. This is most significant where the mold layout requires this varying distribution of material when critical elements, such as the moveable sideliners, are oriented perpendicular to the direction of travel of the feed drawer. If the mold cavities and moveable sideliners are aligned in parallel with the path of travel, then the rigid cut-off bar can be shaped to deposit the correct proportion of material over the area of need, but when the cavities are perpendicular to the feed drawer, there is currently no effective means to accomplish the correct distribution. Currently the methods used in the manufacturing process to aide in material distribution in the mold is to use an agitator grid (an element that sits over the mold box, but under the feed drawer, which functions to create general distribution of the mix material) or to isolate portions of the mold cavities from receiving a percentage of the mix material by use of blank-out plates added to the agitator grid. The blank-out plates are meant to starve some areas of the mold from receiving their full allotment of mix material, while allowing the other areas to receive the full amount. This currently is the known method of distributing material in a mold box.
Generally, after the cut-off bar and feed drawer have returned to their initial starting positions, the vibration cycle begins prior to the stripper shoe compression head, being lowered onto the consolidated material in the mold unit cavities of the mold box assembly. The stripper shoe assembly has plates or stripper shoes mounted to it having the same general plan view shape as the cavities in the mold. The plates may be set in a horizontal or angled orientation, depending on the desired shape for the top plane or surface of the block being made. The plates finalize the compression of the concrete material in the mold prior to pushing or stripping the block unit out of the mold in a downward motion. The stripper shoes are traditionally oriented parallel to the top plane of the mold (generally level or flat), but with some products they may be angled, or patterned in order to add a defined shape to the top surface of the block facing the stripper shoe plates.
The mold box assembly may be agitated to assist in compression of the mix material. Once the vibration cycle is complete, the production pallet is automatically lowered vertically away from the bottom of the mold frame during the de-molding or stripping cycle, and the newly molded block/blocks are pushed downward through the mold so that they remain on the manufacturing pallet in preparation of the next cycle of the manufacturing process were the blocks are sent to a kiln for a curing cycle. Accordingly, the desired shaped blocks can be readily removed from mold cavities.
In commonly assigned U.S. patent application Ser. No. 12/252,837, entitled “RETAINING WALL BLOCK”, the entirety of which is incorporated herein by reference, a mold assembly for use in producing retaining wall blocks has a horizontal planar bottom member, a stripper shoe compression head (also referred to herein as a stripper shoe head assembly), a mold box having a plurality of side walls that define a plurality of mold cavities having open mold cavity tops and open mold cavity bottoms, the horizontal planar member enclosing the open mold cavity bottoms of the plurality of mold cavities and the stripper shoe head assembly enclosing the open mold cavity tops of the plurality of mold cavities during a block forming process. Each of the plurality of mold cavities can be shaped to form a single retaining wall block. Each of the plurality of mold cavities can be oriented such that the first side surface is formed at the bottom of the mold cavity and the second side surface is formed at the top of the mold cavity. One of the side walls of each of the plurality of mold cavities can be moveable from an inward block forming position to a retracted discharge position, the moveable sidewall having a three dimensional surface texture or pattern that imparts to the front face of the retaining wall block the three dimensional surface texture or pattern during the block forming process. The sidewalls of each of the plurality of mold cavities can include a forming channel to shape or form an extending flange or lip element which can be used as a means of connecting courses of the block in a retaining wall assembly, if the blocks are oriented with the flange in a downward position (extending downward past the bottom plane of the retaining wall block). The mold assembly further includes a core forming member which extends vertically into at least one of the plurality of mold cavities to provide the retaining wall block formed therein with a core extending from the first side surface to the second side surface, or can be partially formed from the first surface, but not all the way to the second surface. The core forming member can be configured to form a plurality of cores extending from the first side surface to the second side surface of the retaining wall block and the core or cores can have a variety of shapes, typically selected from round, oval, rectangular and square.
The stripper shoe head assembly includes a lower surface which encloses the open mold cavity tops as the stripping cycle is activated. The lower surface can be angled at an angle α with respect to horizontal such that the second side surface of the retaining wall block formed in each of the plurality of mold cavities during the block forming process forms angle α with respect to the front face of the retaining wall block, and wherein angle α is optimal between about 5° to 20°, or between about 7½° to 15°. Further, the sidewalls of each of the plurality of mold cavities can be shaped to form a vertically extending ridge that provides the retaining wall block with a flange receiving channel formed into a rear portion of the top surface and an upper portion of the rear face of the retaining wall block.
With current feed drawer and cut-off bar distribution techniques, the feed drawer generally distributes the same amount of material to the entirety of each mold cavity. The cut-off bar, which is rigidly coupled to the front of the feed drawer flows over the mold cavity in a horizontal path, with the feed drawer dropping and distributing the mix material as it travels. Once the feed drawer has reached its furthest forward motion point, it retracts along its original path where the cut-off bar now functions to screed or cut-off any excess material that was deposited over the open cavities of the mold, producing a generally level horizontal surface. Typically the mix material is screeded to allow an extra 0.375″ to 1.0″ of extra material over the block mold cavities. This material is the thickness calculated to compress during the vibration and compression cycle, such that the block will be formed in its consolidated state to a pre-determined height in the forming cavity. The stripper shoe head assembly, with angled lower surfaces, descends and encloses the open mold cavities as it finalizes the compression of the material. As the stripper shoe head assembly with angled surfaces lowers to compress the material in the mold cavities, the density of the material is more compressed where the angled surface extends the furthest into the mold cavity and the density of the material is less compressed where the stripper shoe extends into the mold cavity the least. The result is that the block is stronger and denser where the material has been compressed more and is weaker and less dense where the material has been compressed less. This produces an uneven range of density along the gradient where the material was compressed by the stripper shoe head assembly, thus the structural integrity and strength of the block may be compromised which could additionally compromise the structural integrity and strength of any structure made from the blocks. In addition, where the block is over compressed, the material may expand (rebound) when released from the mold cavity and the planer surfaces may tear as a function of this rebound effect. Oppositely, areas in the mold cavity that have not received enough material may be less compressed and have unfilled, broken and crumbling surface areas or edge conditions.
Current feed drawer and cut-off bar distribution techniques do not allow for additional material to be distributed to an area of the mold cavity that may require additional material during compression. This situation arises, for example, in applications where a three-dimensional texture is being imparted onto a surface of the block in the mold cavity. Additional material to fill all crevices and structures of the texture being imprinted may be necessary during compression to ensure that the texture is compacted properly onto the moveable liner which creates the surface of the block being produced. The additional material that is needed where the three-dimensional texture is being imprinted is not needed for the rest of the area of the mold cavity and a material distribution technique that could distribute varying amounts of material throughout a mold cavity would save on material costs while ensuring that the block produced is structurally sound, stronger and more aesthetically pleasing to the eye upon proper imprinting of the texture.
Accordingly, there is a need in the art to correct deficiencies in the distribution of material in a mold box cavity and the amounts of compression within a mold box cavity and to achieve greater overall uniform density of material of the block thus making the blocks stronger and more durable as well as any structure built from the blocks.